a) Field of the Invention
The present invention relates to a metal work drilling tool, and more particularly to a pushing structure of a metal work drilling tool which can effectively control drilling force to improve a drilling efficiency and to reduce a chance that a drill bit is broken due to percussion.
b) Description of the Prior Art
As disclosed by the U.S. Pat. No. 5,439,332 and referring to FIG. 1, a pneumatic spot weld drill 1 is composed primarily of a drill assembly 10, a control valve 12 and a C-arm assembly 14, wherein the drill assembly 10 includes a trigger assembly 101 to supply pressurized gas, a spring 102 which is used to restore a piston assembly 103 and a motor assembly 105 which is provided with an extension rod 104. The motor assembly 105 can be used to rotate a drill bit 106. In addition, by the aforementioned control valve 12, the pressurized gas can be received and controlled to be led to the motor assembly 105, allowing the drill bit 106 to rotate and move. Furthermore, the C-arm assembly 14 is attached on the aforementioned drill assembly 10 and is provided with a locking assembly 140, such that a user can install and dismantle the C-arm assembly 14 as required. When the aforementioned trigger assembly 101 is pressed, the pressurized gas is supplied to the piston assembly 103, thereby pushing the drill bit 106 toward the C-arm assembly 14 and in a mean time, allowing the drill bit 106 to rotate and move.
However, upon using the aforementioned metal work drilling tool 1, following problems and shortcomings actually exist to be improved:                1. As the pushing mode of aforementioned pneumatic spot weld drill 1 utilizes a feed of pressurized gas to move the drill assembly 10 back and forth, pushing force cannot be controlled manually.        2. When the pressurized gas enters into the pneumatic spot weld drill 1, it will supply the drill assembly 10 to move reciprocally and the drill bit 106 to rotate, respectively. Thus, the pressurized gas will be separated into two parts to drive various parts to conduct different usage states, respectively. Therefore, the pushing force of drill assembly 10 will be insufficient, thereby reducing a working efficiency and extending a drilling time.        3. As the drill bit 106 contacts an object for drilling 2 by percussion, the drill bit 106 can be broken easily due to the percussion and therefore the drill bit 106 needs to be replaced frequently, which costs expensively.        
Accordingly, how to eliminate the aforementioned problems and shortcomings of prior art is a technical issue to be solved by the present inventor and related vendors.